The present invention relates generally to the field of optical shutters and switches, and particularly, pertains to optical shutters and switches which operate in the near-infrared and/or visible wavelength regions. More specifically, this invention pertains to optical shutters, switches and buffers comprising a reversible non-reflective-to-reflective optical shutter. This invention also pertains to methods of buffering or storing an optical signal by utilizing the optical shutters and switches of this invention.
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the quantity and speed of data communications over fiber optic systems rapidly increases due to the growing demand from Internet usage and other communications, improved all-optical switching systems are of increased interest to overcome the high cost and slow switching speeds of conventional switches. These conventional switches include, for example, various mechanical switches, electro-optic switches, and thermo-optic switches, such as, for example, described in U.S. Pat. Nos. 5,732,168 and 5,828,799, both to Donald. In particular, the increased complexity and cost of switching systems which involve switching from an optical signal to an electrical signal and then back to an optical signal have increased the level of interest in improved all-optical switches.
An all-optical switch provides switching of an optical signal from one input path to a selected one of a plurality of different output paths without any intermediate conversion of the optical signal to an electrical signal. This is typically accomplished by applying an electrical signal to a switchable element to cause the optical signal to be selectively switched. These electro-optic switches are responsive to the electrical signal to selectively switch the light of the optical signal from the input path to the selected one of the output paths.
A variety of approaches are known for making all-optical or hybrid optical switches, such as, for example, described in U.S. Pat. No. 5,905,587 to Maeno, et al.; U.S. Pat. No. 5,923,798 to Aksyuk, et al.; U.S. Pat. No. 5,970,185 to Baker, et al.; U.S. Pat No. 5,841,912 to Mueller-Fiedler, et al.; U.S. Pat. No. 5,091,984 to Kobayashi, et al.; U.S. Pat. No. 5,406,407 to Wolff; U.S. Pat. No. 5,740,287 to Scalora, et al.; U.S. Pat. No. 5,960,133 to Tomlinson; U.S. Pat. No. 5,539,100 to Wasielewski, et al.; and U.S. Pat. No. 5,943,453 to Hodgson.
The need for improved optical switches is increased by the use of wavelength multiplexing which converts the optical signal in the optical fiber into, for example, 16 signals at 16 different wavelengths in a near-infrared range of about 1540 to 1560 nm, as, for example, described in Bell Labs Technical Journal, January-March 1999, pages 207 to 229, and references therein, by Giles, et al.; and in U.S. Pat. No. 5,959,749 to Danagher, et al. The primary function of the optical switch is to add and/or drop optical signals from the multiple wavelengths traveling through the optical fiber. It would be highly desirable to have arrays of optical switches to handle the optical signals from multiple wavelengths per optical fiber and from multiple optical fibers, such as up to 100xc3x97100 or greater optical switch arrays. Also, it would be highly desirable if the response time for the optical switch is ultrafast, such as 1 nanosecond or less.
It would be advantageous if an all-optical switching system were available which avoided the complexity and cost of optical-electrical-optical (so-called O-E-O) switching systems, conventional electro-optic and other all-optical switching systems while increasing the speed of the optical signal switching times from the millisecond range to the nanosecond or picosecond ranges. It would be further advantageous if an all-optical switching system were available which minimized or eliminated contention among optical signals in fiber optic systems by providing an optical buffer to temporarily store an optical signal for a desired time.
One aspect of this invention pertains to an optical shutter having a first state of a low reflectivity at a range of wavelengths and a second state of a high reflectivity at the range of wavelengths, wherein the optical shutter in the second state comprises an organic free radical compound. In one embodiment, the first state is transparent at the range of wavelengths. In one embodiment, the second state is opaque at the range of wavelengths. In one embodiment, the second state is transparent at the range of wavelengths.
In one embodiment of the optical shutters of this invention, the shutter comprises a first surface layer in the second state, a second surface layer in the second state, and optionally a photon-absorbing layer in an opaque state at the range of wavelengths and interposed between the first and second surface layers, wherein the optical shutter absorbs photons or alternatively, an electrical current is applied, to change at least one of the first and second surface layers to the first state of low reflectivity and to change the optional photon-absorbing layer, if present, to a transparent state at the range of wavelengths; and wherein the optical shutter is reversibly imageable between the first and second states. In one embodiment, the optical shutter absorbs photons to change both of the first and second surface layers to the first state. In one embodiment, the optical shutter responds to the application of an electric current to change both of the first and second surface layers to the first state. In one embodiment, the changes in reflectivity of the first and second surface layers occur at the same time. In one embodiment, one or both of the first and second surface layers of the optical shutter in the second state comprise an organic free radical compound. In one embodiment, the organic free radical compound is reflective at the range of wavelengths.
In one embodiment of the optical shutter of this invention, the imaging from the first state to the second state occurs with no external energy. In one embodiment, the imaging from the first state to the second state is induced by heat. In one embodiment, the imaging from the first state to the second state is induced by absorption of photons from one or more wavelength ranges selected from the group consisting of ultraviolet wavelength ranges, visible wavelength ranges, and infrared wavelength ranges. In one embodiment, the imaging from the first state to the second state is induced by applying an electric current to the optical shutter.
In one embodiment of the optical shutter of the present invention, the optical shutter comprises one or more external energy source elements to provide energy to switch the optical shutter, wherein the one or more external energy source elements are selected from the group consisting of electrical current source elements, heating source elements, ultraviolet light source elements, visible light source elements, and infrared radiation source elements. In one embodiment, the one or more external energy source elements are connected to a control circuit device that monitors the desired timing for providing the energy and delivers a signal to the one or more external sources of energy to provide the energy to the optical shutter.
Another aspect of the present invention pertains to an optical buffer for storing an optical signal for a desired time, which optical buffer comprises two or more optical shutters positioned at one or more first distances and one or more first angles from each other, wherein the two or more optical shutters are imageable and have a first state of a low reflection, such as, for example, no reflection or a reflectance less than 1%, at a wavelength, and a second state of a high reflection, such as, for example, a reflectance greater than 3% or a reflectance greater than 95% at the wavelength, and wherein the two or more optical shutters are reversibly imageable between the first and second states. In one embodiment, at least two of the two or more optical shutters are interposed between an input optical path for the optical signal and an output optical path for the optical signal, and wherein a first imaging between the first and second states of at least one of the at least two of the two or more optical shutters directs the optical signal into storage in an optical buffer path between the input and output optical paths and wherein a subsequent imaging between the first and second states of at least one of the at least two of the two or more optical shutters directs the optical signal from the optical buffer path into the output optical path. In one embodiment, the wavelength is a near-infrared wavelength. In one embodiment, at least one of the two or more optical shutters is interposed between an input optical path for the optical signal and an output optical path for the optical signal, and wherein a first imaging between the first and second states of at least one of the two or more optical shutters directs the optical signal into storage in an optical buffer path between the input and output optical paths and wherein a subsequent imaging between the first and second states of at least one of the two or more optical shutters directs the optical signal from the optical buffer path into the output optical path. In one embodiment, the two or more optical shutters of the optical buffer comprise optical shutters of this invention, as described herein.
Still another aspect of this invention pertains to a method of storing an optical signal in an optical buffer for a desired time, which method comprises the steps of (i) providing one or more optical shutters interposed between an input optical path for the optical signal and an output optical path for the optical signal, wherein the one or more optical shutters are imageable and have a first state of a low reflection at a wavelength and a second state of a high reflection at the wavelength, and wherein the one or more optical shutters are reversibly imageable between the first and second states; (ii) imaging at least one of the one or more optical buffers between the first and second states to direct the optical signal into storage in an optical buffer path between the input and output optical paths; and (iii) subsequently imaging at least one of the one or more optical shutters between the first and second states to direct the optical signal from storage in the optical buffer path into the output optical path. In one embodiment, the one or more optical shutters comprise optical shutters of the present invention, as described herein.
As will be appreciated by one of skill in the art, features of one aspect or embodiment of the invention are also applicable to other aspects or embodiments of the invention.